A&A 619, A70 (2018) Astronomy https://doi.org/10.1051/0004-6361/201731737 & c ESO 2018 Astrophysics

The Hydra I cluster core II. Kinematic complexity in a rising velocity dispersion profile around the cD galaxy NGC 3311 M. Hilker1, T. Richtler2, C. E. Barbosa1,3, M. Arnaboldi1, L. Coccato1, and C. Mendes de Oliveira3

1 European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching, Germany e-mail: [email protected] 2 Universidad de Concepción, Concepción, Chile 3 Universidade de São Paulo, Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Rua do Matão 1226, São Paulo, SP, Brazil

Received 8 August 2017 / Accepted 14 August 2018

ABSTRACT

Context. NGC 3311, the central galaxy of the Hydra I cluster, shows signatures of recent infall of satellite galaxies from the cluster environment. Previous work has shown that the line-of-sight velocity dispersion of the stars and globular clusters in the extended halo of NGC 3311 rises up to the value of the cluster velocity dispersion. In the context of Jeans models, a massive dark halo with a large core is needed to explain this finding. However, position dependent long-slit measurements show that the kinematics are still not understood. Aims. We aim to find kinematic signatures of sub-structures in the extended halo of NGC 3311. Methods. We performed multi-object spectroscopic observations of the diffuse stellar halo of NGC 3311 using VLT/FORS2 in MXU mode to mimic a coarse “IFU”. The slits of the outermost masks reach out to about 35 kpc of galactocentric distance. We use pPXF to extract the kinematic information of velocities, velocity dispersions and the high-order moments h3 and h4. Results. We find a homogeneous velocity field and velocity dispersion field within a radius of about 10 kpc. Beyond this radius, both the velocities and the velocity dispersion start to depend on azimuth angle and show a significant intrinsic scatter. The inner spheroid of NGC 3311 can be described as a slow rotator. Outside 10 kpc the cumulative angular momentum is rising, however, without show- ing an ordered rotation signal. If the radial dependence alone is considered, the velocity dispersion does not simply rise but fills an increasingly large range of dispersion values with two well defined envelopes. The lower envelope is about constant at 200 km s−1. The upper envelope rises smoothly, joining the velocity dispersion of the outer globular clusters and the cluster galaxies. We interpret this behaviour as the superposition of tracer populations with increasingly shallower radial distributions between the extremes of the inner stellar populations and the cluster galaxies. Simple Jeans models illustrate that a range of mass profiles can account for all observed velocity dispersions, including radial MOND models. Conclusions. The rising velocity dispersion of NGC 3311 apparently is a result of averaging over a range of velocity dispersions related to different tracer populations in the sense of different density profiles and anisotropies. Jeans models using one tracer popula- tion with a unique density profile are not able to explain the large range of the observed kinematics. Previous claims about the cored dark halo of NGC 3311 are therefore probably not valid. This may in general apply to central cluster galaxies with rising velocity dispersion profiles, where infall processes are important. Key words. galaxies: clusters: individual: Hydra I – galaxies: elliptical and lenticular, cD – galaxies: haloes – galaxies: individual: NGC 3311 – galaxies: kinematics and dynamics – galaxies: formation

1. Introduction Theclusterenvironmentisclearlyimportantforthebuild-upof such a large halo, either by coalescence of larger galaxies or by the The structure of galaxies can be strongly altered by environ- infall of smaller galaxies or tidal debris of cluster material. This is mental processes, like major and minor mergers, accretion of plausibly also the reason for the immense richness of the globular satellite galaxies, ram pressure stripping and other interactions clustersystems (GCSs)of centralgalaxies (e.g.,Harris et al. 2017) between galaxies and with the intra-cluster medium. A striking and,inthecaseofthisstudy,therichGCSofNGC 3311,thecentral phenomenon in this respect is the existence of very extended galaxy of the Hydra I galaxy cluster (Wehner et al. 2008). stellar haloes around bright central galaxies in galaxy clus- Given that the haloes of massive ellipticals in general grow ters (e.g. Schombert 1987, 1988). Early classification efforts byafactorofabout4inmasssincez = 2(van Dokkum et al.2010), assigned the term “cD” to those galaxies (Matthews et al. 1964; one expects an even higher growth rate in the centres of galaxy Morgan & Lesh 1965) whose haloes can in extreme cases embrace clusters, where the galaxy number density is highest. The more the entire host galaxy cluster as in the case of Abell 1413 (Oemler recent mass growth is dominated by the accretion of low mass sys- 1976; Castagné et al. 2012) frequently also presenting double or tems (minor mergers) which may leave kinematical signatures in multiple nuclei of central galaxies (see Kormendy & Djorgovski the phase space of the outer stellar population of central cluster 1989, for a discussion of the early literature). In the following, we galaxies. These extreme environments, therefore, are suitable to use the term “cD” in this simple sense, irrespective of whether the study the main physical processes that cause the destruction of halo can photometrically identified as a separate entity or not, see infalling galaxies as well as the build-up of the intra cluster light Bender et al.(2015) for a more profound discussion. and the central dark matter halo of a galaxy cluster.

Article published by EDP Sciences A70, page 1 of 23 A&A 619, A70 (2018)

The extended envelopes make it possible to probe the kine- science data were taken in seven different nights between Jan- matical properties of the galaxy light out to large radii. A rise uary 17th and March 29th, 2012, with FORS2 (in multi-object of the velocity dispersion of the galaxy light is not unusual mode, using the Mask eXchange Unit (MXU)) mounted on UT1 for the most massive early-type galaxies (Newman et al. 2013; at Paranal Observatory. We used the 1400V grism, which cov- Veale et al. 2017). The first measured rising velocity disper- ers the wavelength range 4600–5800 Å. With a slit width of sion profile was reported by Dressler(1979) for the cD galaxy 100 and a dispersion of 0.31 Å pixel−1 we reach a spectral res- IC 1101 in the cluster Abell 2029. In the second known and well olution of R = 2100 at 5200 Å, which translates into a veloc- studied case of NGC 6166, the velocity dispersion stays constant ity resolution of ∼140 km s−1. Six different MXU masks were at a value of 200 km s−1 until a radius of 10 kpc and then steeply −1 necessary to cover the halo around NGC 3311. For each mask rises to high values above 800 km s at large radii, reaching the twilight skyflats were taken, mostly in the same nights as the velocity dispersion of galaxies in the cluster (Carter et al. 1999; science exposures. Those flats are important to calibrate the rel- Kelson et al. 2002; Bender et al. 2015). ative responses between object and sky slits. One of the nearest cD-galaxies is NGC 3311, the cen- The mask design follows an “onion-shell” approach. Each tral galaxy in the Hydra I galaxy cluster. Recent publications mask consists of a half-ring of halo slits, all positioned at about on NGC 3311 are mainly from our group (Ventimiglia et al. the same galactocentric distance from NGC 3311. The typical 2008, 2010, 2011; Coccato et al. 2011; Misgeld et al. 2011; dimensions of the slits are 1 × 500. The combination of 2 × 3 Richtler et al. 2011; Arnaboldi et al. 2012; Barbosa et al. 2016, masks with half-rings of slits at different galactocentric distances 2018). Photometric and kinematical studies using the galaxy on each side of NGC 3311 complete the full onion-shell of halo light, planetary nebulae (PNe) and globular clusters (GCs) slits. This is shown in Fig. B.1. The outermost halo slits reach clearly demonstrate the close connection of the inner galaxy distances of 15000(∼35 kpc) from the galaxy centre. The onion- with its host cluster. Asymmetric light distribution and tidal shell approach allows us to study the stellar population proper- tails are evidences of recent infall processes (Arnaboldi et al. ties at several radii as well as at different azimuthal angles in the 2012). Planetary nebulae show a non-Gaussian velocity distri- halo of NGC 3311. It kind of mimics a coarse IFU. The advan- bution with peaks that are offset from the systemic velocity tage of such an approach is that an “effective IFU field-of-view” (Ventimiglia et al. 2011). The central velocity dispersion of the of about 4 × 4 arcmin is homogeneously covered, which is 16× galaxy light is only 150 km s−1 (but fits to its low surface bright- −1 larger than the so far largest single IFU Multi-Unit Spectroscopic ness) and rises up to almost 400 km s within 10 kpc. The more Explorer (MUSE) at the VLT. distant globular clusters reach an even higher velocity disper- The halo slits avoid point sources and galaxies, except the sion, equal to that of the cluster galaxies (Misgeld et al. 2011; lenticular galaxy HCC 007 south of NGC 3311. The position Richtler et al. 2011). To explain this rise with a simple Jeans angle of the masks and thus slits was chosen such that we have model, one needs a large core of dark matter. The population free sky regions close to the borders of the 7.80 field-of-view composition of NGC 3311 indicates a distinction between the in spatial direction of the slits. This is the case north-east and original elliptical galaxy and the later accreted material: the inner south-west of NGC 3311, as can be seen in Fig. B.1. We dis- galaxy is old and metal-rich, while at larger radii the scatter in tributed the sky slits such that they are located at the same metallicity becomes considerably larger (Barbosa et al. 2016). x-positions (in CCD coordinates) as the halo slits. This guar- Apparent discrepancies of kinematical values, in particu- antees that we always have a sky spectrum that covers the lar the velocity dispersion, measured with long-slits of differ- same wavelength range as the corresponding halo spectrum. ent azimuthal orientations have been reported by Richtler et al. We named the slits in the different half-shells with the prefixes (2011). In this paper we demonstrate that indeed the velocity and “cen1”, “cen2”, “inn1”, “inn2”, “out1” and “out2” from inwards velocity dispersion show a two-dimensional irregular pattern and out, and numbered them with increasing spatial position on the that the kinematics at radii larger than 10 kpc cannot be described y-axis of the CCD chip (see Fig. B.1). by a radial coordinate only. This continues the trend already The exposure times of the two innermost shells (cen1 and cen2 seen in the high surface brightness parts of the galaxy, where the and inn1 and inn2) were 2 × 1400 s. The masks of the outer shells dynamical analysis of MUSE observation has revealed an asym- (out1 and out2) were exposed 6 × 1400 s. Between the individual metric velocity and velocity dispersion field with azimuthal vari- exposures a dither along the slit of up to ±0.600 was applied. ations (Barbosa et al. 2018). The present work emphasizes that it Figure1 shows our onion-shell halo slits (in red) in the is important to investigate the entire velocity field of the galaxy context of previous long-slit observations. The blue and green light and its kinematic properties out to large radii. The database slits belong to data presented in Ventimiglia et al.(2010) and of the present paper has already been used in Barbosa et al. Richtler et al.(2011), respectively. Our slit design resulted in (2016), Paper I to analyse the stellar population properties of 135 slits dedicated to the halo of NGC 3311 and NGC 3309. Not NGC 3311. all of them could be used because the 1400 V grism causes a tilt The present paper is structured as follows. In Sect.2 we of the light beam which shifts the spectrum on the detector in Y present the detailed observational properties and data reduction. direction by ∼2800. In this way three spectra, one in each of the The kinematical analysis is described in Sect.3. The measure- masks “cen1”, “cen2” and “inn1”, were lost because they ended ment of stellar kinematics and main results are presented and up in the chip gap of the two FORS2 CCDs. And in the other discussed in Sects.4 and5, with the final summary and conclu- masks six slits, two in each mask, were shorter than expected sion in Sect.6. Throughout this paper, we adopt the distance to because of the gap, and thus the spectra of those slits have a the Hydra I cluster core as 50.7 Mpc. slightly lower signal-to-noise ratio (S/N) than other spectra at similar surface brightnesses. 2. Observations and data reduction 2.1. Observations 2.2. Data reduction For our study of NGC 3311’s halo we used data from The reduction was carried out with custom scripts based ESO programme 088.B-0448 (PI: Richtler). The spectroscopic on IRAF tasks, mainly taken from the twodspec, longslit,

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Fig. 1. Positioning of the slits in the halo of NGC 3311. The small red Fig. 2. Map of the S/N in each region after Voronoi Tesselation of the slits are our novel set of observations, while the two blue and green long whole slit area. The contours show the V-band surface brightness levels −2 slits represent the positioning of previous work by Ventimiglia et al. of objects in the field-of-view ranging from µV = 20−23.5 mag arcsec (2010) and Richtler et al.(2011), respectively. One of the green long in steps of 0.5 mag arcsec−2, from Arnaboldi et al.(2012). slits crosses the neighbouring giant elliptical NGC 3309 north-west of NGC 3311. as the galaxy spectrum. Only then, we subtracted the sensitivity corrected sky spectrum from the galaxy spectrum. Remaining apextract onedspec and packages (e.g. Tody 1993). All science, sky residuals of the 5577.3 Å[O I] sky line were masked out in twilight skyflat and arc lamp exposures were first bias and flat- the final 1-dimensional galaxy spectra. Finally, all spectra were field corrected. Individual twilight skyflats of the same mask corrected for having their wavelength scale in heliocentric veloc- were combined. The science exposures were cleaned from cos- ities, that is the motion of the Sun with respect to the observed lacos spec mics using the _ routine from van Dokkum(2001). We direction as calculated from the header parameters was taken out. determined the spatial distortion of the spectra by identifying We did not perform flux calibration because this is not and tracing the slit gaps in the normalized flatfield as “absorp- straightforward for FORS2/MXU spectra. The standard star is identify reidentify tion features” (using the IRAF tasks , and taken in the middle of the CCD, whereas the MXU slits are dis- fitcoords ). The science exposures, twilight flats and arc lamp tributed all over the CCD. Since the response function depends exposures were then straightened by applying the derived coor- on the x-position on the CCD and all slits cover different wave- dinate transformation. The spectral regions of all individual slits length ranges, most of the extracted spectra would get a slightly were cut out in all rectified frames. An illumination correction wrong and incomplete flux calibrations. In any case, for the pur- of the science exposures and twilight skyflats along the slits was pose of this paper, that is to derive the kinematics of NGC 3311’s applied, which was derived from the twilight skyflats. Next, a halo, a flux calibration is not needed. 2-dimensional wavelength calibration was performed on the arc lamp exposures of each slit and applied to the science exposures. The position of the 5577.3 Å[O I] sky line was used to correct for 3. Stellar kinematics residual zeropoint shifts in the wavelength calibrations, which were of the order of 0.1–0.4 Å. The individual calibrated science We measured the line-of-sight (LOS) stellar kinematics of p exposures of each mask were then averaged. We interactively our dataset using the penalized pixel-fitting code ( PXF, used the IRAF task apall to define the aperture to be extracted Cappellari & Emsellem 2004), which allows the simultaneous in the individual slits, avoiding edge effects. The same extrac- fitting of a linear combination of stellar templates with a line-of- tion was applied to the twilight skyflats. The very central slits sight velocity distribution (LOSVD). We carefully selected the of NGC 3311 as well as the three slits in HCC 007 have a very fitting ranges for each slit individually by eye to avoid continuum high S/N, and we have split them into 2 (central) and 3 and 5 discontinuities, sky lines and strong noise. The overall maximum (HCC 007 outer and inner) sub-apertures, respectively. wavelength range for all spectra is 4510 Å . λ . 5850 Å, but The last, most important step was to subtract the sky from the the selected fitting regions vary depending on the slit positions galaxy spectra, taking into account the different sizes and sen- on the chip, and thus the wavelength region covered. The com- sitivities of the galaxy-sky slit pairs. For that we collapsed for mon minimum range of fitting regions for all spectra is 4900 Å . each slit the 2-dimensional twilight skyflats of the galaxy and λ . 5520 Å. For consistency, we calculated the S/N per Å for all sky slits by averaging all lines along the spatial direction. The spectra in the wavelength range 5200 Å ≤ λ ≤ 5500 Å. We mea- 1-dimensional twilight spectra of galaxy and sky were divided sured the S/N by comparing the integrated light in the observed by each other to derive the relative response between galaxy and spectrum with the standard deviation of the residuals between sky slit. We fitted a spline of 7th order to the response spectrum, the observed spectrum and the best fit template from pPXF. A and used this fit to bring the sky spectrum to the same sensitivity map of the S/N values per spectrum is shown in Fig.2.

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Fig. 3. Six example spectra from high to low S/N(from top left to bottom right panels) together with their pPXF fits (red lines in upper panels) and residuals (lower panels). Apart from the S/N value, the name of the spectrum, the derived radial velocity and velocity dispersion as well as the reduced χ2 value of the fit are given as legend in each panel.

As templates for the spectral fitting we took single stel- tested, in an interactive manner, which combination of additive lar population spectra from Vazdekis et al.(2010), which uses and multiplicative polynomials for the continuum fit in pPXF spectra from the MILES stellar library (Sánchez-Blázquez et al. (adeg and mdeg, respectively) gave the most reliable results. 2006), computed with a resolution of 2.5 Å, a Salpeter initial We chose adeg = 6 and mdeg = 4 for most of the spectra, and mass function (IMF) with logarithmic slope of −1.3, ages from adeg = 8 and mdeg = 2 for some exceptions. The results of kine- 0.1 to 15 Gyr and metallicities in the range −2.3 ≤ [Z/H] ≤ matic measurements with pPXF are presented in Table A.1, and 0.2 dex. We convolved our observed spectra with a Gaussian fil- six example spectra with different S/N values are shown in Fig.3 ter to bring the instrumental resolution of FWHM = 2.1 Å to the together with their best pPXF fits and residuals. resolution of the MILES template spectra of FWHM = 2.5 Å. We produced 2D maps of the kinematic parameters extrap- For the fitting, we used a velocity distribution characterised olating the slits using a Voronoi tesselation (see Fig.4). In all by the velocity (VLOS), the velocity dispersion (σLOS) and the maps the same polygons as shown in the S/N map (Fig.2) are two high order Gauss-Hermite moments h3 and h4, which mea- used. We applied different minimum S/N cuts to the four param- sure deviations from the simple Gaussian profile. h3 describes eters, which are S/N > 5 for VLOS, S/N > 10 for σLOS, and the skewness of the Gaussian, in other words negative values S/N > 15 for the higher moments h3 and h4. Those cuts were indicate a distribution with an extended tail towards low veloci- motivated by visual inspection of the fitting results. Below these ties, and positive values vice versa. h4 describes the kurtosis of cuts the derived values were considered unreliable. the Gaussian, that is positive values describe a distribution more In order to improve the visualization of the main trends in the “peaked” than a Gaussian, and negative values indicate a more maps and to provide a kind of binned 2D map with higher S/N, flat-topped distribution. There is no simple relation between h4 we also produced filtered maps obtained with a locally weighted and the anisotropy. Apart from the anisotropy, h4 depends on scatterplot smoothing (LOESS) algorithm (Cleveland 1979) cal- the potential and the density profile of the tracer population. An culated with the Python implementation of Cappellari et al. exact Gaussian is produced by an isotropic population that gen- (2013). This non-parametric method is suitable for the recon- erates an isothermal potential. struction of functions on noise data, and has a single free param- Besides the best fitting parameters, pPXF also provides a eter, the fraction of data points to be considered around each data noiseless best fit spectrum, and the residual difference between point. We set this fraction to 0.3 for all our maps. For the VLOS the observed and best fit spectrum gives a good estimation of and σLOS maps only regions with S/N > 20 were smoothed, the observation noise. Uncertainties for the four parameters were whereas higher S/N polygons show their original values because calculated via Monte Carlo simulations based on the S/N for their VLOS and σLOS values are highly reliable due to small rela- each spectrum. However, pPXF makes a global minimization in tive errors. For the h3 and h4 maps all polygons were smoothed, the parameter space with a single figure-of-merit function (χ2), thus increasing the signal of structures in adjacent polygon cells and in some cases the “best” parameters are not a good descrip- of the 2D maps and overcoming the large relative errors of h3 tion of the overall shape of the spectra. This issue, the so-called and h4. The smoothed maps illustrate that the small scale varia- template mismatch, can be avoided in most cases by careful tions in the kinematic values do not only depend on the scatter visual inspection of the fitting results. We, therefore, thoroughly of low S/N bins.

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Fig. 4. Kinematic maps of the core of the Hydra I cluster. Upper left panel: line-of-sight recession velocity, VLOS for spectra with S/N > 5 per Å. The results of previous long-slit data (Ventimiglia et al. 2010; Richtler et al. 2011) are shown as well. Upper right panel: line-of-sight velocity dispersion, σLOS. Only results with S/N > 10 per Å are shown. Bottom left panel: higher moment h3 (skewness) for data with S/N > 15. Bottom right panel: higher moment h4 (kurtosis) for data with S/N > 15. In all maps, V-band contours are shown in black, ranging from 20 to 23.5 mag arcsec−2 in steps of 0.5 mag arcsec−2, from Arnaboldi et al.(2012). In all panels, north is up and east is left.

Finally, for the analysis of our results, we overplotted on light close to the lenticular galaxy HCC 007 at the bottom of the these maps two sets of surface brightness contours. The first image. As one can see in Fig.2, also the S /N of our spectra is set was produced from a V-band image in surface bright- enhanced in these excess regions. ness intervals ranging from 20 to 23.5 mag arcsec−2 in steps of −2 0.5 mag arcsec (see Fig.4). The second set was produced from 4. Results the residual V-band image after maximum symmetric models were subtracted from the two central galaxies NGC 3311 and The final kinematic maps are presented in Figs.4 and5. Colour NGC 3309 (Arnaboldi et al. 2012). The contours range from 22 bars in the legend indicate the parameter range displayed in the to 26 mag arcsec−2 in steps of 0.5 mag arcsec−2 (see Fig.5). This individual maps. In order to analyse kinematic trends with galac- residual image clearly shows the non-symmetrical excess of light tocentric distance from NGC 3311 and position angle around it in the north-east region of NGC 3311, as well as some excess of we created position-VLOS and position-σLOS diagrams in four

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Fig. 5. Same as in Fig.4, except that data are smoothed (via the LOESS algorithm, see text) for regions of S/N < 20 in the upper two panels and for all regions in the lower two panels. Moreover, the black surface brightness contours here show the V-band residual map, ranging from 22 to 26 mag arcsec−2 in steps of 0.5 mag arcsec−2, after the subtraction of maximum symmetric models from the two central galaxies NGC 3311 and NGC 3309 (Arnaboldi et al. 2012). In all panels, north is up and east is left.

◦ different segments of 45 width, see Fig.6. The position angle, following error selection for the respective quantity (V, σ, h3 and ◦ ◦ −1 −1 PA, is defined as north = 0 and east = 90 . The four PA values h4): σ(VLOS) < 100 km s , σ(σLOS) < 80 km s , σ(h3) < 0.1 are chosen such that they coincide with the galaxy’s major axis and σ(h4) < 0.1. ◦ ◦ (63 , Arnaboldi et al. 2012), its minor axis (153 ) and the two Moreover, we present in Fig.8 VLOS and σLOS as function of orientations of the long-slits at 108◦ and 198◦ from Richtler et al. position angle around NGC 3311 in four radial bins of 10 kpc (2011), see left panels in Fig.6. Radial bins are also given width from the centre out to 40 kpc. The distributions show in units of effective radii (top labels), with Re = 8.4 kpc for the degree of symmetry and scatter of the LOSVD moments NGC 3311 (Arnaboldi et al. 2012). We corrected for systematic as function of distance to the galaxy centre out to ∼5 effec- velocity offsets between the long-slit and our results, as dis- tive radii. In Figs.6–8, those slits that are dominated by light cussed below. We also produced similar plots for the Gauss- from the giant elliptical NGC 3309 and the lenticular galaxy Hermite coefficients h3 and h4, see Fig.7. In all these plots HCC 007 are indicated by open orange symbols (circles and tri- we only show data (Voronoi tesselation cells) that fulfil the angles, respectively). The selection of those slits was guided by

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Fig. 6. Left panels: line-of-sight velocity as function of galactocentric distance in kpc from NGC 3311 for four conic segments. Red dots and orange open symbols are our measurements, blue squares and green triangles those from long-slit data of Ventimiglia et al.(2010) and Richtler et al. (2011). The orange circles are measurements dominated by the light of NGC 3309, open triangles those of HCC 007. The position angles, PA (north over east) are indicated as legend in the panels. The horizontal dashed line indicates the systemic velocity of NGC 3311 of 3850 km s−1. Middle panels: grey areas show the cones, in which slits have been selected for the left and right plots. Right panels: same as left but for the line-of-sight velocity dispersion. In the left and right panels the distance in units of effective radii is given on the top label. We note that a positive distance in the x-axis of these panels refers to the direction of the position angles as indicated in the plots (north over east), the negative x-axis refers to the opposite PA direction). The axes description of the middle panels are distances in RA and Dec (positive towards north and east, negative towards south and west). The directions of the radial distances along the cones shown in the left and right panels are indicated as black “+” and “−” signs. the surface brightness contours shown in Fig.2. In Table A.1 is rather smooth with indications of a slight “asymmetry” in the the spectra that belong to the halo of NGC 3311, NGC 3309 and sense that VLOS is shifted to higher velocities in the north-east HCC 007 are identified by the flags 1, 2, and 3, respectively, in than in the south-west (see lower left panel in Fig.6). There is, Col. (13). however no sign of ordered rotation around NGC 3311. The sys- Additionally, in order to highlight the asymmetric distri- tem seems to be pressure supported, the velocity dispersion dom- bution of the velocity and velocity dispersion, we plot in inates any potential rotation signal at all radii (see also Sect. 4.5). Figs.9 and 10 folded values for four position angles, overplot- The radial velocities measured in the six most central slits ting the results for the positive major-axis on top of the results (cen1_s27, cen1_s29, cen2_s30 and cen2_s32) are between 3848 from the negative major-axis. We exclude from this plot the data and 3879 km s−1, consistent within the errors with previous mea- points around NGC 3309 and HCC 007, both for our data and surements of NGC 3311’s systemic velocity (e.g. Richtler et al. the longslit data, to only show the profiles of NGC 3311’s halo 2011, but NED: 3825 km s−1). We adopt a central velocity of population. 3863 km s−1 for our work, which is the average value of the six Finally, we analysed the root mean square velocity, rotation central measurements. measure and angular momentum parameter as function of galac- Beyond a galactocentric distance of ∼10 kpc from NGC 3311 tocentric radius in Fig. 12. For that, as well as for the dynami- the velocity field gets inhomogeneous, that is it varies with cal modelling (Sect.5) we apply a more stringent velocity error position angle. Regions of high VLOS values are found around −1 −1 −1 selection, σ(VLOS) < 60 km s , to get a high quality data sam- NGC 3309 (∼4095 km s ) and HCC 007 (∼4760 km s ), which ple. Data points close to NGC 3309 and HCC 007 are excluded is expected due to their higher systemic velocities (see open here as well. orange symbols in Fig.6). It is interesting to note that around HCC 007 there seems to exist a velocity gradient with lower velocities towards NGC 3311 and larger ones away from it (see 4.1. Line-of-sight velocity black line bottom panel of Fig.9). The galaxy HCC 007 itself The velocity (VLOS) map can be characterized by several main shows a clear rotation signal with receding velocities on its (bulk motion) regions, but also considerable velocity variations east side and approaching velocities on the west (see Figs. B.2 on small scales. The velocity field within 10 kpc of NGC 3311 and B.3).

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Fig. 7. Same as Fig.6 for the Gauss-Hermite coe fficients h3 (left panels) and h4 (right panels).

Fig. 8. Left panels: line-of-sight velocity as function of the position angle, PA (north over east), for four radial bins of 10 kpc width between zero and 40 kpc galactocentric distance from NGC 3311, as indicated in the legend of the panel. The radial bins increase from bottom to top. The symbols are the same as in Fig.6. Middle panels: grey areas show the annular areas, in which slits have been selected for the left and right plots. Right panels: same as left, but for the line-of-sight velocity dispersion. In the left and right panels the vertical dashed lines indicate the galaxy’s major axis.

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Fig. 9. Line-of-sight velocity as function of galactocentric radius for Fig. 10. Same as Fig.9 but for the line-of-sight velocity dispersion. four cones of 45◦ width as shown in Fig.6. Black (red) symbols indi- cate the measured velocities for position angles lower (larger) than ◦ 220.5 , and the black (red) solid lines indicate the smoothed velocity 2008; Ventimiglia et al. 2010; Richtler et al. 2011). However, from the LOESS algorithm (see Fig.5). Data points around NGC 3309 the rising σLOS profile varies for different position angles (see and HCC 007 (open orange symbols in Fig.6) were excluded. Figs.6 and 10), meaning that there exist small scale variations of the local velocity dispersion. This also explains the appar- ent discrepancies in the σLOS profiles obtained from the previ- The (south-) eastern halo (70 < PA < 180◦) of NGC 3311 ous long-slit works (see Fig. 4 in Richtler et al. 2011). These is dominated by low radial velocities (see left middle panels in differences vanish when looking at the complete 2-dimensional Fig.6 and black dots in the middle panels of Fig.9). Towards σLOS distribution. The long-slit results from Ventimiglia et al. the north-east, in the region of the excess halo light, velocities (2011) and Richtler et al.(2011) are both consistent with our scatter quite a lot from slit to slit around NGC 3311’s systemic work. velocity (see the left top and bottom panels of Fig.6). In general, The regions of highest velocity dispersions are towards the the velocities derived from previous long-slit work agree very north-east and east of NGC 3311 and in the south next to the well with our velocity map, once systematic offsets to the sys- lenticular galaxy HCC 007 (at PA ∼ 190◦, see bottom right panel temic velocity are corrected for (see left panels of Figs.6 and8). of Fig.6). These regions coincide with the o ffset envelope and Indeed, the long-slit results at PA = 64◦ from Ventimiglia et al. sub-structure from disrupting dwarf galaxies in the Hydra I clus- (2010) show a systematic offset of ∼72 km s−1 (3778 km s−1 ter core, as reported by Arnaboldi et al.(2012). This is also seen close to the centre) with respect to our measurements, whereas in Fig. 10, where outside a radius of ∼10 kpc the average veloc- the central velocity of ∼3864 km s−1 measured by Richtler et al. ity dispersion is higher on the semi-major axis towards north- (2011) is close to our measured value. For Figs.4–8 and9 we east (PA = 108◦) than towards south-west (PA = 288◦). The applied offsets of +72 km s−1 and −14 km s−1 to the long-slit same is true for the directions east and south-east, although the velocities of Ventimiglia et al.(2011) and Richtler et al.(2011), opposite directions are dominated by the low-velocity disper- respectively. sion light of NGC 3309 (see orange circles in the right panels of Figs.6 and8). The high velocity dispersion east of HCC 007 4.2. Line-of-sight velocity dispersion is probably caused by the superposition of the galaxy’s stellar population at high radial velocity (see Fig. B.2) with that of The velocity dispersion (σLOS) of NGC 3311 rapidly increases NGC 3311’s stellar halo at lower radial velocities. with galactocentric distance from ∼185 km s−1 at the centre (slit Low velocity dispersion regions are those around the giant cen2_s32) to ∼500 km s−1 at ∼18 kpc (see Fig.6). This was elliptical NGC 3309 (∼200 km s−1) and HCC 007 (∼80 km s−1), already noted by several previous works (e.g. Loubser et al. which dominate the light in those slits. Curiously, also towards

A70, page 9 of 23 A&A 619, A70 (2018) the north-east (0 < PA < 45◦) there exists a region of relatively low velocity dispersions with σ ∼250–280 km s−1 (see Figs.4 40 5 and5. One might speculate whether the light in those slits is 4 dominated by the pure stellar halo of NGC 3311 or rather cold 30 3 sub-structure in the displaced halo region. 20 We also calculate the second order moment of velocity as the counts 2 log(counts) 10 root mean square velocity: 1 √ 2 2 0 0 Vrms = V + σ , (1) 200 0 200 400 4 2 0 [km/s] log(p-value) where V is defined as |VLOS − VNGC 3311|. Velocity dispersion and Vrms are shown in comparison in Fig. 12 (upper panel). The dif- Fig. 11. Left panel: distribution of observed, but trending corrected, ferences are negligible below 25 kpc and still small beyond that velocity dispersions between 10 and 40 kpc from NGC 3311 (thick radius because V/σ is generally low. We also note that, In the black line) compared to the average distribution of five million reali- case of NGC 3311, V cannot be interpreted as a measure of angu- sations of mock distributions that consider the observational errors only lar momentum (rotation) but describes a velocity bias, since the (grey thin line). Right panel: distribution of five million p-values from the Anderson-Darling test, with the vertical grey line indicating the 5% galaxy itself is displaced in space and velocity from the core of significance level. The significance of an intrinsic scatter in the observed the galaxy cluster (e.g. Barbosa et al. 2018). Thus V cannot rms σLOS distribution is 4.8σ. be applied to our simple dynamical modelling. We, therefore, take the velocity dispersion values for our dynamical analysis in Sect. 5.3. NGC 3311. The left plot shows the distribution of the de-trended reference (observed) sample and the average distribution of five million realisations of the (simulated) comparison sample, The 4.3. Significance of velocity and dispersion scatter right plot shows the distribution of five million p-values from In the sections before we claim to see evidence for an intrin- the Anderson-Darling test, with the vertical line indicating the sic scatter in the radial velocities and velocity dispersions dis- 5% significance level. The low probabilities that both distri- tributions for galactocentric radii >10 kpc. In order to evaluate butions are equal translate into a significance of 5.1σ that the the significance of this intrinsic scatter we statistically compare observed scatter of the σLOS distribution is intrinsic and cannot the distribution of VLOS and σLOS values in the radial range be explained by the observational errors alone. Restricting the 10 < R < 40 kpc with those of five million Monte Carlo real- radial range to 10–20, 10–30 or 15–40 kpc also results in signif- isations that are based on measurement uncertainties only. For icant intrinsic velocity dispersion scatter with σ-values of 3.4, this analysis, we use our error selected sample from Figs.6–10 4.6 and 3.3, respectively. and exclude data points near NGC 3309 and HCC 007. Analogous tests for the distribution of radial velocities lead We use the Anderson-Darling test implemented in the python to a 4.8σ significance of an intrinsic scatter in the velocity dis- package scipy.stats based on Scholz & Stephens(1987) for tribution. Restricting the velocity sample to the east side of the comparison. This test has been shown to perform better NGC 3311, the region that is not influenced by NGC 3309 and than the usually widely used Kolmogorov-Smirnov test (e.g HCC 007, still results in a significance of 3.1σ, despite a lower Mohd Razali & Yap 2011) since it is more sensitive to the differ- number statistics of data points. ences in the wings of the distributions. We test the null hypothe- sis that the distribution and scatter of points is purely caused by 4.4. Higher moments of the line-of-sight velocity distribution measurement errors via this procedure: Firstly, we define the observed distribution of points as func- The higher moments h3 (skewness) and h4 (kurtosis) of the line- tion of radius as our “reference sample”. Then, the null hypoth- of-sight velocity distribution are useful quantities in the case of esis sample, called “comparison sample”, is created from the a relaxed dynamical system. In a pressure supported system with reference sample by assigning a de-trended mean value to each negligible rotation and no orbital anisotropies both moments measurement and adding to it randomly generated gaussian scat- should have values around zero. ter based on its measured uncertainty. The de-trending is done by As can be seen in Figs.5 and7 h3 scatters mostly around an error weighted least square fit to the data. zero, in particular in the central 10 kpc around NGC 3311. In the Secondly, the two distributions are compared via the north-east region of the displaced halo h3 tends to scatter to neg- Anderson-Darling test. If the observed distribution is caused ative values (see left top and bottom panels of Fig.7 for >20 kpc purely by uncertainties then the comparison sample should and <−20 kpc, respectively). It is also mostly negative around be statistically the same as the reference sample. To get the NGC 3309 (see left second panel from top in Fig.7, negative likelihood of how often the comparison sample resembles the spatial axis). That means that the LOSVD has an extended tail observed distribution we generate the comparison sample five towards lower velocities. In the case of NGC 3309 this is proba- million times and obtain p-value distribution of the Anderson- bly due to a contribution of NGC 3311’s halo light to the domi- Darling tests. We compute the probability of the p-value being nating stellar populations of NGC 3309 itself, which has a higher smaller or equal to 0.05, which is 5% significance level that is radial LOS velocity than NGC 3311. In the displaced halo region usually assumed as a statistically significant difference between and east of NGC 3311, radial velocities scatter towards lower two distributions. This takes into account the small number values than the systemic velocity of NGC 3311 (see Fig.6), in statistics and the observation uncertainties. agreement with a negative h3 value. Part of the displaced halo Finally, we compute the significance of the deviation in terms light and dwarf galaxy tidal tails seem to be dominated by low- of sigma, assuming a gaussian distribution. radial velocity stellar populations. In Fig. 11 we show the results of our tests for the distribu- The moment h4 is, with a few exceptions, always positive tion of velocity dispersions in the radial range 10–40 kpc from (see Figs.5 and7). At face value this points to radially biased

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In our case, we calculate V/σ for each Voronoi bin/slit indi- vidually and evaluate its trend with galactocentric distance to NGC 3311. V is defined as |VLOS − VNGC 3311| and σ is the aver- age of the line-of-sight velocity dispersion in the respective bin. For λR, we calculate the local angular momentum parameter λ(R) as RV λ(R) = √ , (2) R V2 + σ2 and the cumulative angular momentum parameter λ(

A70, page 11 of 23 A&A 619, A70 (2018) or nearly flat velocity dispersion profiles from central values of clean dynamical interpretation. For NGC 6166 we predict a sim- ∼240 km s−1 to ∼350 km s−1, similar to the values of NGC 3311 ilar complex velocity dispersion field as found for NGC 3311. at the same distance. But it is is not clear what is their kinemati- cal behaviour outside 2–3 effective radii, where the velocity dis- persion profile of NGC 3331 is rising to the level of 500 km s−1 in 4.7. Results in context of cosmological simulations its outer halo. Galaxies with a mildly rising velocity dispersion The growth of massive early-type galaxies appears to happen profiles are NGC 1129 and NGC 7242. However, it is striking in two main phases. The early mass assembly (2 < z < 6) that some galaxies show a large scatter in their dispersion profile is dominated by significant gas inflows (e.g. Kereš et al. 2005; (NGC 3158, NGC 507, NGC 1016), indicating that Jeans models Dekel et al. 2009) and the in situ formation of stars. The late evo- with one Jeans equation only (unique density profile, anisotropy, lution is dominated by the assembly of stars which have formed etc.) may not be appropriate. in other galaxies and have then been accreted via interactions or Also other kinematical studies of massive galaxies are con- mergers on to the central galaxy at lower redshifts (0 < z < 1) sistent with the occurrence of flat and rising velocity dispersion (e.g. Meza et al. 2003; Naab et al. 2007). profiles (Carter et al. 1999; Kelson et al. 2002; Loubser et al. The cosmological simulations of this two-phase galaxy for- 2008; Coccato et al. 2009; Pota et al. 2013; Forbes et al. 2016). mation process by Oser et al.(2010) predict that the present Loubser et al.(2008) presented radial profiles for the line-of- day masses of very massive galaxies is dominated at the level sight velocity and velocity dispersion from long-slit observations of 80% by accretion and merging since redshift z ≤ 3. Also of 41 BCGs, most of which they classify as dispersion supported, Rodriguez-Gomez et al.(2016) showed, using the Illustris sim- and which also show a variety of dispersion profile shapes, with ulations, that 80% of the stars in very massive galaxies (M∗ ∼ 12 a fair fraction of galaxies with flat or rising dispersion profiles, 10 M ) are born ex situ and then were accreted onto the although not with the same amplitude of ∼600 km s−1 as for galaxies via mergers. This means that the outer stellar dynam- NGC 3311. ics of a central massive galaxy are dominated by the orbits Newman et al.(2011) find the BCG in A383 to exhibit a of accreted material. In particular, minor mergers of galaxies steeply rising dispersion profile that climbs from ∼270 km s−1 embedded in massive dark matter haloes provide a mechanism at the centre of the galaxy to ∼500 km s−1 ∼22 kpc, a similar for explaining radially biased velocity dispersions at large radii behaviour as for NGC 3311. Forbes et al.(2016) compared 24 (Hilz et al. 2012). Also cosmic zoom simulations of massive early-type galaxies from the SLUGGS survey to the assembly galaxies (Wu et al. 2014) show that massive galaxies with a large classes of galaxy simulations by Naab et al.(2014), see also fraction of accreted stars have radially anisotropic velocity distri- Sect. 4.7. They assign 6 galaxies to the classes C, E and F, butions outside the effective radius. Naab et al.(2014) presented which are the most appropriate to describe a massive, central a two-dimensional dynamical analysis of a sample of 44 cosmo- slow rotating galaxy. In therms of the high-order moments h3 logical hydrodynamical simulations of individual central galax- 11 and h4, the kinematic properties of NGC 5846, a central group ies up to 6 × 10 M . They defined the classes A-F to char- galaxy, seems to show most similarity to NGC 3311, followed acterise the different assembly histories. NGC 3311 is different by NGC 4374 and 4365, although their velocity dispersion pro- than most types. If any, type C or F is closest to the properties of files are not rising but are rather flat. NGC 3311 (see Table 2 of Naab et al.): map feature is a disper- Positive h4 values at all radii have also been found for sion dip, no correlation of h3 with ν/σ. the three BCGs NGC 6166, 6173 and 6086 in the study of Groenewald et al.(2017) investigated the mass growth of Carter et al.(1999) . Also most galaxies in the MASSIVE sur- BCGs since redshift z < 0.3. They found an increasing pair vey show positive average h4 values (Veale et al. 2017). Positive fraction, with decreasing redshift, which they interpret as an h4 values generally indicate a bias towards radial orbits (Gerhard increasing merger fraction. The mass growth via accretion from 1993; Rix et al. 1997; Gerhard et al. 1998). Since h4 stays nearly close pairs is 24 ± 14% since z = 0.3. Most of this mass is constant at a value of ∼0.1 at all radii, the increase in velocity deposited into the intracluster light. NGC 3311 has the close pair dispersion is not associated with a change in velocity anisotropy NGC 3309. Although no direct interaction signs are seen in our towards tangential orbits. It rather reflects an increasing mass- data, it is plausible that some outer material of NGC 3309 has to-light ratio, and thus a massive dark halo. already been stripped off in the cluster potential and might con- The lack of a significant rotation signal for NGC 3311 is tribute to the central cD halo in the future. consistent with the view that most BCGs are slow rotators, Ye et al.(2017) used the Illustris simulations to investigate mostly due to their build-up from multiple (dry) mergers. In a the displacement and velocity bias of central galaxies with VIMOS IFU study of 10 BCGs at redshift z = 0.1 with masses respect to their dark matter haloes. The central galaxy veloc- 10.5 11.9 10 < Mdyn < 10 M , Jimmy(2013) found that 70% are ity bias can be explained by the close interactions between the 11.5 slow rotators, and above Mdyn ∼ 10 M all BCGs are slow central and satellite galaxies. A central velocity bias naturally rotators. The steadily increasing cumulative angular momentum leads to a small offset between the position of the central galaxy profile of NGC 3311 lies above most radial profiles of BCGs and the halo potential minimum (Guo et al. 2015). This scenario from the MASSIVE survey (Veale et al. 2017). might explain the offset halo we see around NGC 3311. The probably two best studied cases of central galaxies with rising velocity dispersion profiles in their outer halo that are sim- 5. Discussion ilar to NGC 3311 are M 87 in the Virgo cluster and NGC 6166 in Abell 2199. Murphy et al.(2014) measured the line-of-sight In Paper I, where we analysed the metallicity, [α/Fe] abundances velocity distribution from integrated stellar light at two points and ages of the stellar halo light around NGC 3311, we con- in the outer halo of M 87. They found a rising velocity disper- cluded that our findings can be explained by a two-phase galaxy sion up to 577 km s−1, but argue that there is evidence for two formation scenario (e.g. Oser et al. 2010). The inner spheroid kinematically distinct stellar components. They conclude that component (within 10 kpc) was probably formed in-situ in a the asymmetry seen in the velocity profiles suggests that the rapid collapse very early-on, whereas the outer halo was accreted stellar halo of M 87 is not in a relaxed state and complicates a over a long timescale, a process that is still ongoing. Do we also

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Table 1. Projected velocity dispersions for the stellar population (s), globular clusters (gc), and galaxies (gal).

Pop. Distance σLOS ∆σLOS Ngal (kpc) (km s−1) (km s−1) (1) (2) (3) (4) (5) s 4.04 267 20 s 5.12 288 20 s 7.52 335 20 s 10.50 380 20 s 11.61 407 20 s 12.90 416 20 s 14.30 436 20 s 16.90 454 20 s 18.50 470 20 s 20.20 484 20 s 21.50 495 20 s 23.80 515 20 s 25.67 524 20 s 28.07 540 20 s 30.12 551 20 s 31.92 554 20 gc 13.900 535 70 gc 31.3 567 71 gc 38.30 650 77 gc 52.20 732 97 gc 55.70 707 89 gc 97.50 807 107 gc 195.00 703 94 gal 150.00 697 79 39 gal 250.00 798 122 27 gal 350.00 664 73 41 gal 450.00 699 90 30 gal 550.00 725 82 43 gal 650.00 603 83 27 Fig. 13. Upper panel: all galaxies within a distance of one degree from gal 750.00 1050 200 15 NGC 3311 with a radial velocity limit of 20 000 km s−1. The Hydra I members stand out clearly. We select galaxies with a radial velocities less than 6000 km s−1. Lower panel: surface number densities in 8 bins. see this in the kinematical features of the galaxy? Another impor- The parameters of two modified Hubble profiles are given, one of them tant question is whether Jeans models are appropriate for con- fitted with the first bin skipped. The core radius is only badly defined and may be high. straining the mass profile when phase space is clumpy.

5.1. The velocity dispersion profile from stars to galaxies derived in the following manner: we selected from the NASA Extragalactic Database all objects classified as galaxies within Richtler et al.(2011) presented velocity dispersions of bright a radius of one degree around NGC 3311, corresponding to globular clusters around NGC 3311 and, in conjunction with 885 kpc (there are hardly any objects outside), and end up with long-slit data of the central galaxy population, constructed spher- 638 galaxies. These galaxies are nicely stratified in redshift. ical Jeans models. Figure 4 in Richtler et al.(2011) indicates a The Hydra I members stand out clearly as the upper panel of rising velocity dispersion, which may be understood as a class Fig. 13 shows (for readability only until 20 000 km s−1 as the attribute of central cluster galaxies. A spherical Jeans model in maximal radial velocity). We select Hydra I members as having conjunction with a unique tracer population demands a massive radial velocities less than 6000 km s−1. This sample comprises dark halo with a large core in order to explain the rising disper- 251 galaxies. We build 8 bins of widths 100 km s−1 and calcu- sion profile. late the surface number density as shown in the lower panel of Because we want to discuss our results in the context of the Fig. 13. entire cluster, including the galaxy population, Table1 lists the The surface number densities are fit by the modified Hubble relevant velocity dispersion values for the inner stellar popu- profile lation, the globular clusters, and the cluster galaxies. The first column indicates the population, the second the cluster-centric n0 n r ( ) = 2 −c (4) distance, the third and forth the velocity dispersion and its uncer- [1 + (r/rc) ] tainty, and the fifth column with the number of galaxies in the bin, as detailed below. with rc as the core radius. Two fits, one skipping the inner- The quoted values for stars and globular clusters come from most bin, are indicated. The important point is that the core Richtler et al.(2011). The values for the galaxies have been radius is not well constrained. At larger cluster-centric distance

A70, page 13 of 23 A&A 619, A70 (2018) it may assume values even above 300 kpc. This must be remem- lower envelopes of this distribution are quite well defined. The bered when constructing Jeans models, because the core radius lower envelope is constant at a velocity dispersion of 200 km s−1 is related to the difference in the gravitational potential experi- and it traces remarkably well the MONDian prediction (see enced by a tracer population: a small core radius means a small magenta curve in Fig. 14), with few exceptions. The upper enve- −1 0.59 potential difference, a large core radius a large potential differ- lope follows (r in kpc), σupper[km s ] = 170 × (1 + (r/rc) ), ence. For each bin we calculate the velocity dispersion apply- with rc = 7.3 kpc (dashed line in Fig. 14). This also fits well ing the maximum likelihood velocity dispersion estimator and the globular cluster velocity dispersions out to 100 kpc (see its uncertainty given by Djorgovski & Meylan(1993). Fig. 15), which reaches maximum values of ∼800 km s−1. In both (Figs. 14 and 15) only data points with a velocity dispersion error smaller than 60 km s−1 have been considered. 5.2. A MONDian model Our central claim is that this scattered distribution of the The mass profiles of galaxy clusters argue for the existence of velocity dispersion values can be explained by a large range of cluster dark matter even with the validity of MOdified New- mass profiles, depending on the properties of the tracer popula- tonian Dynamics (MOND; e.g. Milgrom 2015) and it is clear tions. Figure 14 (small scale) and Fig. 15 (large scale) illustrate that a rising velocity dispersion in NGC 3311 strongly con- this claim by showing two extreme models. Plotted are Jeans tradicts MONDian predictions at first sight. However, we find models using the stellar mass profile from Richtler et al.(2011). it interesting where MOND appears in our context. Therefore The surface brightness profile is we briefly summarise how we calculate the MONDian circular   !2α1  !2α2  velocity. Our technique is described, for example, for the case   R   R   µV (R) = −2.5 log a1 1 +  + a2 1 +   (8) of NGC 4636 by Schuberth et al.(2006, 2012) and we refer the   r1   r2   interested reader to these works. −8 −9 00 00 Significant MONDian effects are expected, when the accel- with, a1 = 2.602 × 10 , a2 = 1.768 × 10 , r1 = 5 , r2 = 50 , 2 eration, g = Vcirc/R, is smaller than the constant a0 = 1.35 × α1 = α2 = −1.0. This has to be multiplied with the stellar M/LR −8 −2 10 cm s (Vcirc is the circular velocity and R the galactocen- ratio. Here we adopt 5.0 instead of 6.0 which better represents tric radius). The recipe for calculating the MONDian circular the central velocity dispersion. In the upper panel isotropic mod- velocity gM from the Newtonian circular velocity gM in case of els are included while in the lower panel radially biased models sphericity is are shown, where we adopt the anisotropy to be 1 r gN = µ(g/a0)gM (5) β(r) = (9) 2 r + rs where the function µ interpolates between the Newtonian and the MONDian regime. We chose the “simple” formula, µ = x/(x + (formula (60) of Mamon & Łokas 2005) with some small rs so 1), with x = gM/a0. that practically β = 0.5 over the entire radius range. We consider the baryonic mass profile as the sum of Model 1 (red curve) is the sum of the stellar mass and the the stellar NGC 3311 mass profile and the X-ray mass after Burkert-halo of dark matter whose density profile is Hayakawa et al.(2006) which we compute as ρ ρ(r) = 0 (10) 2 3 2 Mx(r) = 4π × n0 × (rc r + rc arctan(r/rc)) (6) (1 + r/rc)(1 + (r/rc) ) −4 −3 with ρ being the central density and r a characteristic radius. with n0 = 1.59 × 10 M pc and rc =102 kpc. The MONDian 0 c circular velocity then follows as As a second reference model, we choose a model for MOND (magenta curve; e.g. Milgrom 1984, 2014). The favoured mass r q model for NGC 3311 in Richtler et al.(2011) is clearly non- 2 4 2 vM = vN(r)/2 + vN(r)/4 + vN(r)a0r. (7) MONDian, but the new view onto the phenomenon on a rising velocity dispersion may not longer permit to see NGC 3311 as a The difference between the purely baryonic mass and the MON- clear-cut example for a galaxy that needs dark matter beyond the Dian mass is called the “MONDian ghost halo”. The projected MONDian ghost halo. velocity dispersions are then calculated as in any Jeans model. Model 3 (green curve) is the stellar mass only, which we give for comparison. 5.3. The velocity dispersions and comparison with models 5.4. Meaning of the velocity dispersion pattern We want to argue with the help of Fig. 14 that the infer- ence of a cored dark matter profile may provide only a partial Within a spherical Jeans model, each coordinate communicates description of the dynamical state of the system. The velocity with all other coordinates by an infinite number of tracers follow- field clearly depends on position angle, but the one-dimensional ing a uniform density profile. Here we have a different situation presentation of the profile shows a pattern that is easily over- in that we obviously observe the transition from a small scale to a looked in two-dimensional maps. The description of our mea- large scale potential that means different populations with differ- surements (including Richtler et al. 2011) is: within the inner ent dynamical histories, their superposition and their projection. 5 kpc, the dispersion rises from a central value of 170 km s−1 to This transition will not be sudden, but smoothed out during the 250 km s−1. That can be explained by the baryonic mass pro- entire history of infall processes (e.g. see the properties of the file in conjunction with a small radial anisotropy. At radii larger phase space for BCGs in the simulations by Dolag et al. 2010). than 5 kpc, the velocity dispersion is no longer a unique func- At a given radius, the minimum velocity dispersion must tion of radius, but spreads out in some dispersion interval whose describe an in situ population whose dynamics is not influ- size increases with radius. This feature is already insinuated in enced by the cluster potential, but by the local distribution Fig. 4 of Richtler et al.(2011). One notes that the upper and of mass, where contributions come from orbits within about

A70, page 14 of 23 M. Hilker et al.: Kinematic complexity around the cD galaxy NGC 3311

Fig. 14. Spherical Jeans models for the line-of-sight velocity dispersion Fig. 15. Spherical Jeans models for the line-of-sight velocity disper- of our NGC 3311 halo population data (with flag = 1 in Table A.1) as sion of several tracer populations as function of galactocentric distance function of galactocentric distance to NGC 3311 for the isotropic (top to NGC 3311 for the isotropic (top panel) and partly radial (bottom panel) and partly radial (bottom panel) case. The green curve shows the panel) case and different core radii as indicated (blue lines). The aster- baryonic component only (stellar mass with M/LR = 5.0 and mass of isks mark the upper envelope of the stellar light σLOS distribution from X-ray gas). The magenta curve is a MOND model. The red curve is our data (dashed line in Fig. 14). Filled circles represent the velocity the sum of the baryonic mass (green) and a Burkert halo. See text for dispersions of globular clusters, and squares the velocity dispersion of more details on the models. In the upper panel the dashed line is an Hydra I cluster galaxies. The dashed (green) lines are MOND models. approximate fit to the upper envelope of the distribution. For comparison, we also show as red lines the cored Burkert haloes from Richtler et al.(2011) for the extreme core radii. 10–20 kpc. Quickly overlapping and becoming visible outwards of radius r = 10 kpc, one finds populations whose dynamical galaxies a fit to the sample of Christlein & Zabludoff (2003) histories are progressively stronger linked to the large-scale clus- yields 286 kpc. Any other tracer population assumes values in ter potential. The highest dispersion values must be caused by between these extremes. the largest potential differences and naturally elongated orbits. Figure 15 illustrates this scenario by displaying the measure- Because of the projection of radially varying fractions of dif- ments from the centre to the cluster regime. We plot all available ferent sub-populations (e.g. galactic stars, cD halo stars, intra- velocity dispersion measurements: asterisks are the upper enve- cluster stars) one also finds velocity dispersion values in between lope from Fig. 14, filled circles represent globular clusters from the minimum and the maximum dispersion values. Richtler et al.(2011) and Misgeld et al.(2011), filled squares From these considerations, one would conclude that mass represent the galaxy sample from Christlein & Zabludoff (2003). determinations based on Jeans-models with a single tracer pop- We evaluated the velocity dispersions of the galaxies employing ulation are in our case not appropriate. The actually observed the dispersion estimator from Djorgovski & Meylan(1993). projected line-of-sight velocity distribution is a superposition of One can see in Fig. 15 that beyond 40 kpc the upper envelope several, maybe many, populations with different samplings of the of the velocity dispersion of the stellar light smoothly blends galaxy and cluster potential, disturbing a “clean Jeans-world”. into the rising velocity dispersion profile of globular clusters, reaching maximum values of ∼800 km s−1 at 100 kpc. Outside this radius, the velocity dispersion profile of cluster galaxies 5.5. An illustration for the scatter of velocity dispersions stays flat with high values between 600 and 800 km s−1 out to 700 kpc from the cluster centre. The upper panel in this figure Given the considerations above, the dark matter halo of shows isotropic models, the lower panel the same radial bias Richtler et al.(2011) is an ingredient to fullfil the Jeans-equation as in Fig. 14. The solid (blue) lines are models assuming as for one given population. a mass profile the sum of the hydrodynamic X-ray mass pro- We assume that the projected density profiles of the inner file and the stellar mass in order to have a good approximation stellar population and the cluster galaxies as the extreme pop- −1 for small radii, where the X-ray mass fails. The dashed (green) h 2i ulations can both be described by ρ ∝ (1 + (r/rc) , where lines are MOND models. The four values in parsecs to the left rc is the core radius. The size of rc then indicates the differ- of the upper panel correspond sequentially to the core radii. ent potentials the populations are living in: a large core radius The red lines in both panels are the cored Burkert haloes from means that many objects with orbits with large “apocluster” Richtler et al.(2011) for the extreme core radii. distances are sampled, a small core radius means that mainly Even a mass profile like the one suggested by MOND may the “local” population is contributing. The core radius for the produce the full range of observed velocity dispersions, depend- stellar population is 1.1 kpc. On the other hand, for the cluster ing on the properties of the tracer population, which obser-

A70, page 15 of 23 A&A 619, A70 (2018) vationally are not directly accessible. The cored dark halo of 200 km s−1, fitting well to the MONDian expectation. The upper −1 0.59 Richtler et al.(2011) may owe its existence only to the assump- envelope can be written as, σupper[km s ] = 170×(1+(r/7.3) ) tion of a uniform density profile of the tracer population. (r in kpc), which quite precisely connects the stars with the glob- However, the cluster galaxy sample is not well described by ular cluster population. the MOND models. A thorough discussion is beyond the scope Given the infall processes, we interpret this behaviour as of our paper, but we note that the classical assertion that galaxy the superposition of various tracer populations. Tracer popu- clusters need dark matter even with the validity of MOND may lations can probe strongly varying potential differences within merit further investigation. Galaxy clusters are anyway not in the cluster depending on their spatial distribution. We explain the deep MOND regime, but in the transition region where some the fact of a minimum and a maximum velocity dispersion at a arbitrariness regarding the exact behaviour exists (with the mass given radius by a minimally concentrated population (the cluster of Fig. 15, the acceleration at 100 kpc is 1.3 × a0, at 1 Mpc galaxies) and a maximally concentrated population (the stars of 0.2 × a0), with a0 being the acceleration threshold in the MOND NGC 3311’s inner spheroid). Between these extremes, all dis- −8 −2 prescription (a0 ∼ 10 cm s ). persion values are possible. In the transition zone we sample Furthermore, we probably oversimplify the MONDian with increasing radius more and more radially biased popula- model by assuming a continuous mass distribution and neglect- tions with a shallow distribution. A long-slit average over all ing galaxy interactions. In addition, we assume that the X-ray populations thus results in a rising velocity dispersion. gas constitutes the entire baryon content. Finally, galaxy infall Under these circumstances, the potential cannot be precisely into a cluster does not start from zero velocity, but already with constrained except for the very inner region (where baryons velocities corresponding to the large scale structure, that in turn dominate) and for the large scale galaxy potential. Previous must be studied under MOND conditions (Candlish 2016). statements about dark haloes are probably not valid. We show with Jeans models that a range of mass profiles can generate all observed projected velocity dispersions depending on the core 6. Conclusions and summary radius of their distribution. The MOND mass profile is also capa- NGC 3311 is the central galaxy in the Hydra I galaxy clus- ble of producing the inner dispersion values, but fails in case ter. Previous work revealed much evidence for matter infall of the cluster wide potential. We caution, however, that a more from the cluster environment from galactocentric radii of about trustworthy test needs to be done in order to probe the formation 5–10 kpc outwards. As for other central galaxies, a globally of the galaxy cluster under MOND conditions. photometrically distinct halo is not discernible, but the velocity With the increasing availability of large field IFUs more dispersion of the stellar population, and at larger radii the veloc- galaxies will be observed. We predict that the increasing scatter ity dispersion of globular clusters, rise from the central value of dispersion values will emerge as a characteristic for those cen- of about 180 km s−1 to about 800 km s−1 characterising the clus- tral galaxies with rising velocity dispersion profiles. The cored ter’s galaxy population. In the framework of Jeans models this dark halo of Richtler et al.(2011) may owe its existence only behaviour is best explained by a large cored halo of dark mat- to the assumption of a uniform density profile of the tracer ter. Seemingly conflicting long-slit measurements of the velocity population. dispersion caused the wish for a more complete measurements of the velocity field. Acknowledgements. We would like to thank the anonymous referee for his/her In order to find kinematic signatures of sub-structures around very valuable comments. Based on observations collected at the European NGC 3311 we used FORS2 in MXU mode to mimic a coarse Organisation for Astronomical Research in the Southern Hemisphere under ESO “IFU”. Our novel approach of placing short slits in an onion programme 088.B-0448(B). This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Lab- shell-like pattern around NGC 3311 allowed us to measure its oratory, California Institute of Technology, under contract with the National 2D large-scale kinematics out to ∼4–5 effective radii (∼38 kpc). Aeronautics and Space Administration. T. R. acknowledges support from the This is the first time that kinematic maps for a central galaxy are BASAL Centro de Astrofísica y Tecnologias Afines (CATA) projects PFB- measured out to that radius. 06/2007 and AFB-170002, and from FONDECYT project Nr. 1100620. T. R. thanks ESO/Garching for a science visitorship during May-September 2016. These data show that the velocity field becomes inhomoge- C.E.B and C.M.dO. thank the São Paulo Research Foundation (FAPESP) fund- neous at about 10 kpc, slightly outside the effective radius of ing (grants 2011/21325-0, 2011/51680-6, 2012/22676-3 and 2016/12331-0). NGC 3311. 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A70, page 17 of 23 A&A 619, A70 (2018) 4 h cient; (9) Gauss-Hermite ffi coe adeg mdeg flag 27d31m41.13s in kpc; (5) position 3 h − = ) N 1 / − S 4 h 156068 92.5 54.7 6 6 4 4 3 3 100 55.2 6 4 3 199113 14.3 13.4 6 6 4 4 1 2 056 19.1 6 4 1 048 24.0 6 4 1 026 46.9 6 4 1 024 44.6 6 4 1 029 52.1 6 4 1 017 73.7 6 4 1 010 131.1 6 4 1 037 41.2 6 4 1 010 120.6 6 4 1 010 121.1 6 4 1 011 113.3 6 4 1 024 62.3 6 4 1 017 63.2 6 4 1 024 54.0 6 4 1 024 63.5 6 4 1 028 40.0 6 4 1 036 33.4 6 4 1 058051 24.1 21.7 8 6 2 4 1 1 046 25.5 6 4 1 043 24.0 6 4 1 031 35.4 6 4 1 025 42.3 6 4 1 033 32.8 6 4 1 019 67.8 6 4 1 029 42.8 6 4 1 017 68.8 6 4 1 009 109.8 6 4 1 029 24.4 6 4 1 011 114.7 6 4 1 ...... 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 035 047 001 008 002 101 013 138 087 015 122 085 017 062 065 098 102 028 268 120 050 078 027 043 043 162 109 285 035 086 143 139 082 124 095 ...... 0 0 0 0 10h36m42.71s and Dec − − − − = 3 h 110 0 072 066 0 053 052 061 0 035 0 025 0 022 0 024 0 015 0 009 0 032 0 009 0 009 0 009 0 023 0 017 0 025 0 023 0 029 0 039 0 078 0 043 045 0 052 0 033 0 025 0 032 0 019 0 026 0 016 0 008 0 029 0 009 0 ...... 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 132 008 103 056 064 065 175 067 045 142 073 039 024 014 012 023 019 002 053 039 012 013 010 028 051 023 003 006 027 015 120 002 007 010 006 ...... 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 − − − − − − − − − − − − − − − − − − − − − − − − ) (Å 8 0 7 0 3 0 3 3 3 6 0 8 0 8 3 3 1 13 10 47 30 28 0 20 12 11 10 16 14 15 0 12 19 0 17 28 0 29 37 40 22 12 0 15 17 13 0 − ± ± ± ± ± ± ± ± ± ± ± LOS ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± σ 7 54 66 69 70 42 322 2624 214 281 22 348 9 280 9 306 9 262 6 287 2 203 16 335 2 195 2 195 2 193 11 349 5 253 13 459 9 307 17 402 14 283 25 250 3033 411 452 31 443 18 395 10 378 14 305 7 268 14 380 6 295 2 215 10 280 2 201 ) (km s 1 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± − LOS V ) (km s ◦ 27d33m36.4s27d33m32.0s 29.6 28.0 130.9 129.8 4858 4867 27d32m33.4s 19.2 111.3 4136 27d32m04.6s27d32m24.7s 21.4 14.5 99.7 108.0 4031 3970 27d32m10.7s 13.0 102.3 3796 27d31m56.6s 10.6 96.3 3866 27d31m52.3s 6.9 94.5 3874 27d31m34.3s 10.2 86.7 3895 27d31m35.8s 6.6 87.3 3884 27d31m42.2s 2.0 90.1 3851 27d31m16.7s 10.3 79.1 3886 27d31m34.7s 2.3 86.8 3879 27d31m35.6s 2.0 87.2 3879 27d31m33.7s 2.7 86.4 3885 27d31m09.5s 8.9 76.2 3914 27d31m17.4s 6.2 79.4 3926 27d31m05.9s 8.9 74.7 3943 27d31m10.6s 9.2 76.6 3955 27d30m59.4s 11.6 72.1 3935 27d30m47.5s 14.0 67.6 3888 27d30m27.4s 18.4 60.5 3906 27d30m49.7s27d31m01.9s 17.7 18.5 68.4 73.1 3948 3878 27d31m12.7s 17.2 77.5 3860 27d31m12.0s 14.2 77.2 3896 27d31m24.2s 11.2 82.3 3965 27d31m38.6s 10.4 88.5 3899 27d31m36.5s 6.9 87.6 3917 27d31m52.0s 9.8 94.3 3859 27d31m48.4s 6.1 92.8 3872 27d31m41.9s 1.5 90.0 3862 27d32m06.4s 9.8 100.5 3942 27d31m47.3s 1.7 92.3 3848 27d33m34.2s 28.8 130.4 4895 − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − (J2000) (J2000) (kpc) ( N per Å; (11) additive polynomial for continuum fit in pPXF; (12) multiplicative polynomial for the continuum fit in pPXF; (13) flag: 1 - belongs to NGC 3311, 2 - belongs to / Measured kinematic properties around NGC 3311. IDcen1_s14a RA 159h10m08.4s Dec R PA cen1_s14bcen1_s14c 159h10m04.8s 159h10m12.0s (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) cen1_s18 159h09m43.2s cen1_s19cen1_s20 159h09m18.0s 159h10m01.2s cen1_s21 159h09m57.6s cen1_s23 159h10m01.2s cen1_s24 159h10m15.6s cen1_s25 159h10m01.2s cen1_s26 159h10m15.6s cen1_s27 159h10m33.6s cen1_s28 159h10m08.4s cen1_s29 159h10m48.0s cen1_s29a 159h10m46.9s cen1_s29b 159h10m49.1s cen1_s30 159h10m26.4s cen1_s31 159h10m48.0s cen1_s32 159h10m44.4s cen1_s33 159h11m02.4s cen1_s34 159h11m02.4s cen1_s35 159h10m58.8s cen1_s36 159h10m48.0s cen1_s37cen2_s21 159h11m31.2s 159h11m45.6s cen2_s22 159h11m45.6s cen2_s23 159h11m31.2s cen2_s25 159h11m24.0s cen2_s26 159h11m24.0s cen2_s27 159h11m09.6s cen2_s28 159h11m20.4s cen2_s29 159h11m06.0s cen2_s30 159h10m48.0s cen2_s31 159h11m13.2s cen2_s32 159h10m37.2s Columns: (1) slit ID; (2) centre of slit right ascension; (3) centre of slit declination; (4) radial distance to NGC 3311 at RA cient; (10) S ffi angle to the centre ofcoe NGC 3311 (from north to east); (6) heliocentric line-of-sight recession velocity; (7) line-of-sight velocity dispersion; (8) Gauss-Hermite NGC 3309, 3 - belongs to HCC 007. Appendix A: Results table Table A.1. Notes.

A70, page 18 of 23 M. Hilker et al.: Kinematic complexity around the cD galaxy NGC 3311 adeg mdeg flag ) N 1 / − S 4 h 011 113.8 6 4 1 011 115.5 6 4 1 028 37.6 6 4 1 043042 17.7 30.3 8 6 2 4 1 1 021 66.1 6 4 1 056051 25.2055 20.3054 6 19.9 6 22.6 6 4 6 4 4 1 4 1 1 1 030 37.7 6 4 1 072 33.7 6 4 1 028 48.5 6 4 1 061034 18.1067 29.0034 6 21.1048 6 43.9044 6 25.0 4 6 30.5 4 6 4 2 6 4 1 4 1 4 1 1 1 043 27.8 6 4 1 045 29.2 6 4 1 044 30.4 6 4 1 040 43.1 6 4 2 054 16.6 6 4 1 037050 25.8 18.2035 6 6 29.1 4 6 4 1 4 1 1 069 16.0 8 2 1 051 29.1026 6 62.2 4 6 1 4 2 059 86.5 6 4053053 3 18.7 26.4 6 6 4 4 1 2 081 39.4 6060 4 14.2 3 6 4 1 084 44.4055078 6 16.8 15.0 6 4 6 4 3 4 1 1 ...... 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 094 097 032 067 046 078 126 047 045 159 010 114 012 073 069 082 111 130 114 007 110 052 133 004 073 219 153 043 180 090 096 044 152 077 093 033 053 153 ...... 0 0 0 0 0 − − − − − 3 h 009 0 010 0 027 0 019 0 057 040 0 030 0 061085 0 114 0 042 0 0 026 0 046 034 0 057 038059 0 036 0 055 0 043 0 045 0 037 0 075 0 033 0 063 0 043074 0 026 0 036 0 0 037 0 049 0 046 0 080061 0 0 077 0 103059 0 069 0 ...... 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 020 005 029 045 038 078 179 074 052 061 058 103 042 077 009 004 021 024 039 088 017 120 047 048 010 047 087 059 009 004 012 034 102 040 020 015 108 109 ...... 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 − − − − − − − − − − − − − − − − − − − ) (Å 3 3 7 0 8 5 0 8 0 1 11 13 0 12 0 15 18 74 0 53 10 0 43 0 4044 0 32 0 35 0 33 2447 0 22 0 43 0 22 0 25 0 20 16 45 0 12 23 20 2327 0 43 70 0 52 30 − ± ± ± ± ± ± LOS 432 – – 12.5 8 2 1 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± σ ± 2 185 2 200 10 276 5 224 36 603 10 270 3435 312 32 250 39 413 478 9 278 29 329 15 273 214117 388 32 429 351 23 416 25 356 284 14 241 24 276 56 558 13 241 46 426 347 360 10 210 225 3 59 18 336 15 320 4 69 1823 235 320 7 70 32 312 65 417 154 203 4744 403 420 ) (km s 1 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± − LOS V ) (km s ◦ 27d31m48.1s 2.0 92.6 3851 27d31m46.5s 1.4 91.9 3848 27d32m13.2s 9.2 103.3 3933 27d32m08.2s 6.5 101.2 3867 27d31m01.6s 17.1 73.0 3820 27d32m18.2s 8.9 105.4 3874 27d30m23.8s27d30m08.6s27d30m49.7s 23.727d31m05.5s 29.9 59.3 21.7 54.7 3993 21.2 68.4 4144 74.5 3927 3711 27d32m13.2s 8.6 103.3 3895 27d30m37.8s 21.0 64.1 4015 27d32m24.7s 10.9 108.0 3895 27d30m47.9s27d30m29.5s27d30m44.6s 14.427d30m23.8s 19.6 67.727d30m45.4s 14.1 61.227d30m29.9s 3907 19.3 66.5 4070 16.4 59.3 3894 19.0 66.8 4021 61.3 3961 3975 27d32m23.6s 12.1 107.5 3891 27d30m39.2s 20.0 64.6 3978 27d32m41.3s 15.3 114.2 3926 27d30m58.0s 14.7 71.5 3940 27d32m32.6s 16.5 111.0 3827 27d31m26.4s27d31m10.2s 15.827d30m49.7s 19.6 83.3 76.4 4039 21.4 4062 68.4 4061 27d33m45.0s 30.5 133.0 4531 27d31m37.6s 16.227d31m12.4s 88.1 4011 15.4 77.3 3987 27d33m47.5s 31.2 133.6 4564 27d31m51.2s27d31m57.0s 21.6 16.6 94.0 96.5 4117 3908 27d33m42.5s 29.8 132.4 4566 27d32m19.3s 17.8 105.8 3911 27d32m43.1s 24.1 114.9 4131 27d32m26.2s27d32m40.6s 30.627d32m15.7s 108.5 21.0 3839 21.4 113.9 104.3 4092 3902 − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − (J2000) (J2000) (arcsec) ( continued. IDcen2_s32a RA 159h10m36.2s Dec R PA (1)cen2_s32b 159h10m38.2s (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) cen2_s33 159h11m02.4s cen2_s34 159h10m44.4s inn2_s20 159h11m38.4s cen2_s35 159h10m44.4s inn1_s37inn1_s39 159h11m38.4s inn2_s18 159h12m00.0s inn2_s19 159h11m52.8s 159h12m00.0s cen2_s36 159h10m26.4s inn1_s36 159h11m38.4s cen2_s37 159h10m30.0s inn1_s30inn1_s31 159h10m19.2s inn1_s32 159h10m08.4s inn1_s33 159h10m44.4s inn1_s34 159h10m33.6s inn1_s35 159h11m16.8s 159h11m09.6s cen2_s38 159h10m15.6s inn1_s29 159h09m50.4s cen2_s39 159h10m22.8s inn1_s28 159h10m01.2s cen2_s40 159h09m57.6s inn1_s24inn1_s25 159h09m39.6s 159h09m28.8s inn1_s27 159h09m32.4s cen2_s45a 159h10m26.4s inn1_s23 159h09m36.0s inn1_s26 159h09m46.8s cen2_s45b 159h10m22.8s inn1_s20inn1_s21 159h09m14.4s 159h09m36.0s cen2_s45c 159h10m30.0s inn1_s19 159h09m39.6s inn1_s16 159h09m25.2s inn1_s15 159h08m45.6s inn1_s17inn1_s18 159h09m39.6s 159h09m21.6s Table A.1.

A70, page 19 of 23 A&A 619, A70 (2018) adeg mdeg flag ) N 1 / − S 4 h 044064 146.1077 175.8 6047 171.1 6038 110.5 6056 100.6 4 6053 4 10.0 6130 4 12.5 3 091 6 4 15.5 3 058 6 4 11.8 3 043 6 18.1 3 4040 6 38.7 3 4016 6 42.9 4029 1 6 77.4 4032 1 6 46.2 4021 1 6 36.2 4048 1 6 47.4 4045 2 6 18.3 4100 2 6 28.1 4055 2 6 13.4 4052 2 6 10.0 4085 2 6 4 9.6 2 6 4 6.8 2 6 4 2 8 4 2 2 4 2 2 1 1 058073 17.5078 20.8050 6 13.3062 6 18.6062 6 14.8 4080 8 20.7 4036 6 13.8 4116 1 6 27.6 2046 1 6 16.6 4089 1 6 27.3 4044 1 6 14.6 4062 1 6 24.7 4052 1 6 14.9 4091 1 6 20.0 4051 1 6 14.4 4119 1 6 18.7 4 1 6 16.7 4 1 6 4 1 6 4 1 4 1 4 1 1 1 ...... 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 053 080 097 084 057 125 051 057 116 108 158 075 071 086 098 074 160 119 091 032 161 094 071 029 038 140 051 072 105 113 027 038 002 050 135 155 030 262 025 ...... 0 0 0 0 0 0 0 0 − − − − − − − − 3 h 034041 0 044 0 030 0 026 0 133 0 075106 0 076046 0 045 0 032 0 014 0 026 0 029 0 019 0 045 0 040 0 087 0 050 0 085 0 152 0 136048 0 051 0 060115 0 047059 0 040 0 088 0 040 051039 0 073 0 084 0 097 0 067049 0 106 0 – 21.4 6 4 1 ...... 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 012 008 022 021 043 017 098 161 193 056 170 056 036 102 025 137 115 105 041 039 010 127 039 040 038 050 066 086 016 040 081 009 055 175 043 022 142 164 019 034 ...... 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 − − − − − − − − − − − − − − − − − − − − − − − − ) (Å 8 0 54 0 58 0 7 7 0 1 10 87 38 61 56 2316 0 12 12 2116 0 37 0 0 49 96 0 3233 0 24 0 62 3056 0 45 40 27 9821 0 28 60 43 39 − ± ± ± ± ± ± ± LOS ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± σ 453 91 3 88 117 71 36 706 81 78 336 50 358 20 376 12 290 11 214 3 235 69 196 5 180 18 240 13 212 283 30 225 95 218 38112 336 526 – 0 5 114 2432 426 27 204 60 404 27 480 48 427 34 440 41 306 23 280 99 274 24 – – 0 0 8419 441 33 220 46 318 47 584 36 321 104 413 – ) (km s 1 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± − LOS V ) (km s ◦ 27d33m42.1s27d33m39.6s27d33m44.3s 30.227d33m36.7s 29.4 132.327d33m15.5s 30.7 131.7 4749 27d32m51.7s 28.6 132.8 4759 27d32m22.2s 34.6 131.0 4749 27d32m30.8s 34.1 125.3 4762 27d31m49.1s 36.2 117.9 4113 27d31m55.6s 30.2 107.0 3745 27d31m23.2s 36.6 110.3 4002 27d31m28.6s 30.5 4009 93.127d30m58.7s 36.8 95.927d30m47.5s 4211 30.5 81.927d30m36.4s 4093 37.2 84.227d30m15.5s 4096 37.3 71.827d30m23.8s 4097 32.8 67.627d29m58.9s 4095 35.6 63.527d29m52.1s 4056 27.6 56.727d30m02.2s 4056 34.4 59.327d29m40.6s 4071 34.5 52.0 4084 28.0 50.2 4141 34.0 52.9 5280 47.4 4052 4940 27d33m41.0s 29.8 132.1 4747 27d32m25.8s27d32m44.2s27d32m35.5s 14.327d32m51.7s 19.5 108.427d32m37.0s 14.1 115.2 3972 27d32m55.3s 18.4 112.1 3755 27d32m39.5s 13.6 117.9 3800 27d32m55.7s 18.0 112.6 3859 27d32m46.7s 16.4 119.1 3866 27d33m26.3s 19.0 113.6 4028 27d33m08.3s 19.8 119.2 3918 25.8 116.1 3734 23.8 128.3 3982 123.2 4488 3445 27d31m28.6s27d31m55.2s27d31m53.4s 16.027d32m13.9s 21.2 84.227d32m09.6s 15.9 95.727d32m30.1s 3851 20.7 94.9 3908 15.5 103.6 3921 19.6 101.8 3842 110.0 3955 3292 27d31m34.0s 21.1 86.5 4256 − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − (J2000) (J2000) (arcsec) ( continued. inn2_s39binn2_s39c 159h10m15.6s inn2_s39d 159h10m19.2s inn2_s39e 159h10m15.6s out1_s13 159h10m22.8s out1_s14 159h08m56.4s out1_s15 159h08m42.0s out1_s16 159h08m20.4s out1_s17 159h08m49.2s out1_s18 159h08m13.2s out1_s19 159h08m38.4s out1_s20 159h08m13.2s out1_s21 159h08m38.4s out1_s22 159h08m16.8s out1_s23 159h08m20.4s out1_s24 159h08m45.6s out1_s25 159h08m45.6s out1_s26 159h09m21.6s out1_s27 159h09m07.2s out1_s28 159h09m14.4s out1_s29 159h09m46.8s 159h09m36.0s inn2_s39a 159h10m19.2s inn2_s22inn2_s23 159h11m45.6s inn2_s24 159h12m07.2s inn2_s25 159h11m45.6s inn2_s26 159h12m00.0s inn2_s27 159h11m38.4s inn2_s28 159h11m45.6s inn2_s29 159h11m20.4s inn2_s30 159h11m31.2s inn2_s31 159h11m02.4s inn2_s32 159h11m09.6s inn2_s33 159h10m37.2s inn2_s34 159h10m44.4s inn2_s35 159h10m08.4s inn2_s36 159h10m19.2s inn2_s37 159h09m54.0s inn2_s38 159h10m30.0s 159h09m57.6s (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) IDinn2_s21 RA 159h12m07.2s Dec R PA Table A.1.

A70, page 20 of 23 M. Hilker et al.: Kinematic complexity around the cD galaxy NGC 3311 adeg mdeg flag ) N 1 / − S 4 h 080081 13.8055 7.4091 6 21.7053 6 8.9056 6 20.9 4093 8 9.7081 4 6 13.7 4051 1 17.7 6046 2 6 11.0 1 4068 1 6 20.6250 4 6 11.3 1 4060 1 6 15.5 4109 6 12.0 1 4086 1 6 14.5 4048 1 6 15.2 4080 1 6 14.5 4116 1 8 4 5.7051 1 6 4 4.6 1 6 2 6.6063 1 6 4 1 12.8 6060 1 4084 1 4 8 12.0044 4 1 7.7052 6 16.7 1 2088 10.5 1 6043 6 16.7 4058 1 6 15.0101 4 6 22.3 4052 1 6 20.9 4062 8 27.5 1 4 1 6 16.4 4 1 6 2 1 6 4 1 4 1 4 1 1 1 ...... 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 12 . 075 154 047 120 155 107 009 151 070 124 088 002 148 025 007 051 026 106 023 068 052 099 217 017 144 121 025 255 091 ...... 0 ...... 0 0 0 0 0 0 0 0 0 0 0 0 0 0 − − − − − − − − − − − − − − − 3 h 077 141 077125 0 050130 0 078063 0 085 0 048074 0 069 055053 0 051 0 066046 0 086 051 0 041 0 120 205 052104 0 052 0 049 0 109 0 051 046155 0 ...... 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 040 068 013 056 180 007 055 193 004 079 096 065 156 134 094 012 036 149 085 040 014 021 000 007 097 062 040 113 254 012 ...... 0 0 0 0 0 0 0 0 0 0 0 0 − − − − − − − − − − − − ) (Å 1 7747 0 31 0 8267 0 38 53 48 40 37 37 0 7373 0 8090 0 0 78 0 58 55 0 67 − LOS 119 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± σ ± 85 635 6628107 342 58 275 533 5051 846 108 292 57 1000 348 3248 451 25 437 79 403 105 116 706778 630 139 – 680 – 93 0 30064300 – –94 0 95 – 0 –66 535 0 114 – 324 –77 0 7879 635 57 – –55 – 501 0 87 445 0 – – 395 0 – – 0 7.8 – 6 5.2 6 4 4 1 1 ) (km s 1 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± − LOS V ) (km s ◦ 27d29m32.6s27d29m53.9s27d29m28.7s 33.327d30m01.1s 26.6 45.627d29m32.3s 32.8 50.727d29m53.9s 3828 28.0 44.727d30m10.8s 3974 33.0 52.627d30m54.4s 4485 33.3 45.527d30m36.4s 3668 33.9 50.727d31m26.8s 3613 37.0 55.327d31m18.8s 3844 29.3 70.1 3878 37.1 63.5 3546 30.4 83.4 3977 80.0 3532 3883 27d29m56.8s 26.7 51.4 4296 27d31m53.4s27d31m47.3s27d32m08.9s 37.027d32m06.0s 29.8 94.927d32m34.4s 34.9 92.327d32m46.0s 4904 29.5 101.527d32m37.3s 3678 36.6 100.3 3948 27d33m06.5s 36.1 111.7 3434 27d32m59.3s 29.6 115.9 3591 27d33m24.5s 35.6 112.8 3598 27d33m12.2s 27.6 122.6 2261 27d33m35.3s 34.5 120.4 3923 27d33m23.0s 27.2 127.8 3795 27d33m46.4s 33.3 124.4 4034 27d33m28.1s 26.6 130.7 3765 27d33m52.2s 33.2 127.5 4383 27d33m20.5s 26.2 133.3 3930 27d33m13.7s 32.6 128.8 4267 27d33m52.2s 25.9 134.6 3688 27d33m26.6s 27.2 126.8 3778 32.7 124.8 4305 32.4 134.6 3931 128.4 4985 4104 − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − (J2000) (J2000) (arcsec) ( continued. out1_s31out1_s32 159h10m01.2s out1_s33 159h10m48.0s out1_s34 159h10m33.6s out1_s35 159h11m34.8s out1_s36 159h11m16.8s out2_s13 159h12m03.6s out2_s14 159h12m25.2s out2_s15 159h13m04.8s out2_s16 159h12m21.6s out2_s17 159h13m12.0s 159h12m43.2s ID RAout1_s30 159h10m15.6s Dec R PA (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) out2_s18out2_s19 159h13m12.0s out2_s20 159h12m43.2s out2_s21 159h13m01.2s out2_s22 159h12m39.6s out2_s23 159h13m01.2s out2_s24 159h12m54.0s out2_s25 159h12m28.8s out2_s26 159h12m39.6s out2_s27 159h12m03.6s out2_s28 159h12m18.0s out2_s29 159h11m45.6s out2_s30 159h11m56.4s out2_s31 159h11m20.4s out2_s32 159h11m34.8s out2_s33 159h10m51.6s out2_s34 159h11m06.0s out2_s35 159h10m04.8s out2_s36 159h09m39.6s out2_s37 159h10m15.6s 159h09m21.6s Table A.1.

A70, page 21 of 23 A&A 619, A70 (2018)

Appendix B: Additional figures and the mask names colour-coded, to ease the identification of spectra in the text and Table A.1. Figures B.2 and B.3 show the velocity field and LOSVD The first additional figure (Fig. B.1) highlights the adopted onion higher moments of and around the Hydra I cluster lenticular shell observing strategy with six different mask sets of half-rings galaxy HCC 007, which seems to interact with NGC 3311 as (three on each side of the galaxy). The slit numbers are given, judged from a wide tidal tail feature east of the galaxy.

cen1

40 39 41 38 cen2 47 44 43 42 37 45 inn1 4847 46 50 5349 44 56 54 43 42 inn2 40 52 555148 46 45 52 51 50 1 12 out1 1 2 2 1046 44 3 out2 49 47 41 3 4 48 33 3 5 35 31 4 15 29 6 7 43 18 2 45 14 17 5 36 41 1640 32 27 8 38 30 26 4 6 4013 34 28 13 39 7 24 5 9 20 8 37 33 25 9 1442 35 36 31 6 7 38 10 13 15 23 36 29 1615 34 32 8 1739 18 37 35 30 27 22 9 14 19 28 21 2120 34 12 2019 32 30 10 22 23 24 33 26 25 1111 17 31 28 12 19 25 24 16 22 22 20 21 2929 26 25 26 27 23 0 30 27 19 29 3232 17 18 24 28 24 20 Y [kpc] 23 23 21 18 12 21 31 19 20 26 34 22 21 11 25 33 36 15 18 10 35 19 17 40 38 41 43 15 13 48 9 28 37 20 15 14 47 27 16 13 10 22 40 18 11 8 24 30 32 1241 39 34 17 29 16 23 36 10 7 31 14 33 35 16 6 26 42 9 11 7 20 25 38 9 8 28 35 5 13 6 34 27 30 3 32 37 374212 6 49 4 29 14 7 5 4 39 8 45 46 31 4 3 33 44 36 5051 52 3 1 53 54 2 5556 57 58 2 59 60 61 1 44 62 46 4748 51 63 45 54 55 49 51 40 50 53 52 52 43 50 38 43 39 48 49 40 4142 45 47 44 46

40 20 0 20 40 X [kpc]

Fig. B.1. Finding chart for slits. Different masks are colour-coded. The names of the masks are given in the legend on the upper right.

A70, page 22 of 23 M. Hilker et al.: Kinematic complexity around the cD galaxy NGC 3311

Fig. B.2. From top left to bottom right panels: line-of-sight velocity, velocity dispersion, moments h3 (skewness) and h4 (kurtosis) in the sub-sections of the three slits on top of the lenticular galaxy HCC 007. Adjacent slits on NGC 3311’s halo are also shown. The rotation signal of HCC 007 is clearly visible in all maps.

Fig. B.3. From top to bottom panels: line-of-sight velocity, velocity dis- persion, moments h3 (skewness) and h4 (kurtosis) as function of isopho- tal distance from HCC 007.

A70, page 23 of 23